viernes, septiembre 17, 2010
Wonders of the Solar System - The thin blue line (III)
I came to Cape Town in South Africa (…) I am about to fly incredibly high, to the very edge of the Earth’s atmosphere. From here I am hoping to see something something that only a handful of people have ever seen. The thin blue line, the fragile strip of gas that surrounds our whole planet. And this is what is going to take me there… an English Electric Lightning. (…) This piece of magnificently overpowered engineering is going to take me 18km straight up.
Above me the sky is a deep dark blue. And that is what I’ve come to see. Our atmosphere
It acts as a soothing blanket that traps the warmth of the sun, yet protects us from the harshness of its radiation. (...) The oxygen and water that the atmosphere holds plays a fundamental role in the ongoing survival of millions of different species living on the planet.
All atmospheres in the Solar System are unique. But the ingredients and forces that shape them are universal. At the heart of each is the glue which holds the Solar System together, a fundamental force of nature: gravity. (…) Earth has enough mass to keep a tight grip of the gas molecules that make up our atmosphere. It holds them against the surface and allows us to breathe.
The air pressure is pushing up as well as down… there’s no problem in holding the water in the glass.
If you ask yourself the question: Why is the Earth the temperature that it is? Then, the obvious answer may seem to be… well, because it’s 150 million km away from the Sun. But actually thing aren’t quite that simple.
This is the Namib desert in Namibia in Southwestern Africa. And as the sun sinks below the horizon, the temperature from day to night can be as much as 30ºC. (…) the reason is that this is also one of the driest places on the planet. And so, there is very little water vapour in the atmosphere. That means that the atmosphere is not a very good insulator. And so when the Sun disappears the heat just disappears quickly into space.
Now, there’s a planet in the Solar System (…) where the temperature shift between day and night it’s not a mere 30ºC, but an immense amount bigger (…) Mercury: This tortured piece of rock suffers the biggest temperature swifts of all the planets. From 450ºC in the day to -180ºC at night. And all because Mercury has been stripped naked. It has virtually no atmosphere at all. Like all planets of the Solar System, Mercury had an atmosphere when it was formed, but it lost it very quickly. (…) The bigger the planet, the stronger the gravitational pull, and the easier it is for the planet to keep hold of its atmosphere. So Mercury was too small, and too hot, to hang on to its Atmosphere.
This is Saskatchewan in western Canada (…) In November 2008 a piece of asteroid, a space rock, weigthing about ten tons entered the atmosphere right over here. (…) what was unusual about this one was that it was over a quite a densely populated area (…) and it was captured by a lot of CCTV cameras. (…) They show the meteorite as it stripped across the sky at 20 km per second. It was brighter than the moon and turned the night sky blue.
-Here there is one!
-It’s been completely rounded off. The heat melted the surface of the rock. How hot does something have to be to do that?
-6.000ºC will do it…
The Earth was spared this colossal impact by nothing more than a tenuous strip of gases that surrounds us. But not all planets have this protective blanket. When a meteorite hits naked Mercury, there is no atmosphere to brake it up or slow it down. (…) For the last 4.6 billion years Mercury has been bombarded with countless asteroids and comets. (…) Craters, inside craters, inside craters.
Venus and Earth share many similarities (…) But Venus is a tortured world, where thick clouds of sulphuric acid are driven along by high speed winds and temperatures are hot enough to melt lead. All because this planet’s atmosphere created a runaway greenhouse effect. (…) Venus’s atmosphere was flooded with greenhouse gases. The nearby Sun slowly boiled away its oceans, pumping water vapour into the atmosphere. And Carbon dioxide from thousands of erupting volcanoes added to the stifling mix.
Namib desert is not the hottest or driest desert in the world. But these are some of the oldest sand dunes in the world. (…) This is what the Surface of Mars looks like.
There is a vehicle running across the surface of the red planet today. A space rover named Opportunity. (…) Mars has vast dunes, enormous volcanoes and giant ice sheets. It has canyons and river valleys. Mars is a dry, frozen version of our home, covered in red dust and sand. And it’s all due to the fact that Mars has virtually no atmosphere.
But there are clues that things weren’t always this way. (…) These images caused quite a lot of excitement, because of this rock [which] is an iron nickel meteorite and it’s about 60cm across, weights half a ton. It came from space, through Martian atmosphere and landed on the ground. (…) It must be than in the past, Mars’s atmosphere was significantly denser. (…)
Why did Mars loose its thick atmosphere? There are many ways in which a planet can loose its atmosphere (…) In the case of Mars it’s thought that, one of the dominant mechanisms was in the interaction with the solar wind. (...)
As the [melted iron] core spins, it generates a magnetic field which shoots out from the pole and cocoons the whole planet. This magnetic shield is strong enough to deflect most of the solar wind that comes our way. (…)
At some point in the past, Mars would also have had a molten core, and did have a magnetic field. But because Mars is a smaller planet than the Earth, it lost its heat more quickly, the core solidified, the electric currents could no longer flow and its field vanished.
Tormentas en Júpiter
Weather is a feature of every planet with an atmosphere. (…)
To experience the most extreme and violent weather in the Solar System, we need to travel to Jupiter. (…) Its atmosphere is many thousands of kilometres thick and in a constant state of motion. (…) Yet, this alien world shares a feature with our own planet: electrical storms. (…)
The physics of storms on Jupiter is, of course, the same as on Earth. Warm, moist air deep in the atmosphere starts to rise, and as it rises, it cools, and the moisture condenses out to form clouds. Now, that rising up leaves a gap beneath it, a low pressure area, so more warm, moist air is sucked in and that fuels the rise of the storm. (…)
On Earth, those storm systems are powered by the Sun. But the storms on Juipiter are far more powerful, and its five times further away from the Sun (…)
As you go deep into Jupiter’s atmosphere something very interesting happens to those gases [hydrogen and helium] (…) 20.000km beneath the surface, the pressure is so high that gases are transformed into a strange metallic liquid. As the gases are squeezed, a vast amount of energy is released, enough energy to fuel some of the biggest storms in the Solar System. The biggest of them all is the Big Red Spot.
Saturn’s moon Titan is unique, because of that, [an atmosphere] 1000 km deep, 4 times denser than the atmosphere of the Earth. (…) Titan has the most earthlike atmosphere in the entire Solar System. A thick blue line, rich in nitrogen and containing methane. At first sight, a world this small shouldn’t be able to hold on to such a dense atmosphere, except Titan lies in one of the coldest regions of our Solar System, and that makes all the difference. (…) Hot gases have more energy to escape a planet’s gravitational pull than cold gases.
In 1997 Cassini began its jurney to Titan. It carried with it the Huygens probe, a lander to set down on this frozen moon. (…) These are the actual images taken by Huygens as it slowly parachuted to the surface.
It was amazing, because we had no idea what to expect (…) Then these first pictures came back and it was astonishingly familiar. (…) I can see here, and that is what it actually looks like. (…) [Rocks] are smooth, and it looks like they had been eroded by tumbling water, similar to stones found in river beads here on Earth. (…) Evidence of flowing rivers had never been found before on a moon. But it wasn’t the only surprise…
This is the Matanuska glacier in Alaska. (…) This hold landscape is testament to the erosive power of this stuff.. this mixture of ice and rock that rolls down this valley over hundreds of thousands of years. (…) Our planet is just the right temperature and pressure to allow water to exist as solid, as liquid, and as gas.
The atmosphere in Titan is the perfect temperature and pressure, to allow something to exist, that has never been seen before on a world beyond Earth. (…)
The interesting thing is this black blob here. (…) There is only one really good explanation to that. That is, that they are incredibly flat surfaces. In fact they are surfaces of liquid. (…) This is the first evidence of a lake in a body other than the Earth. But these lakes, can’t be of course lakes of liquid water… but then, what is it?
The floor of this lake is covered in rotten vegetation. (…) That is being broken down by bacteria to produce a gas that bubbles off from the floor of the lake. That gas is methane. (…) In Earth it can only exist as a highly flammable gas. But Titan’s temperature and atmospheric pressure is perfect to allow methane to exist as a solid, a gas, and most importantly, a liquid. So the images that Cassini captured were gigantic lakes of liquid methane. (…) This is Kraken Mare, an over 4000km2, is the biggest body of liquid on Titan. It’s almost five times the size of lake Superior. (…)
Where we have clouds of water, Titan has clouds of methane, with methane rain. Where we have lakes and oceans of water, Titan has lakes of liquid methane. (…) On Titan the Sun lifts the methane from the lakes and saturates the atmosphere with methane. (…)
And rain would be absolutely magical sight on Titan, because the atmosphere is so dense and the gravity of the moon is so weak, the drops of methane rain would grow to over a centimetre in size and they would fall to the ground as slowly as snowflakes in our own planet.